A Motorola Droid 4 (SLIDE IN KEYBOARD FUCK YES) with a 5" screen and more recent components. Hell, use mid-high end from 2018, like 3GB RAM and a decent processor would be more than enough for me. Don’t forget the earphone jack and easily removable back.
In the realm of pure fantasy, a stealth boy from Fallout, or the similar Stealth thingy from Metal Gear Solid